A United Nations report says more than 3,000 civilians died in Afghanistan's conflict last year, the worst annual toll in the decade-long war.

The U.N. Assistance Mission in Afghanistan said Saturday that 3,021 civilians were killed in 2011, an 8 percent increase over the previous year, and the fifth year in a row that the death toll has risen.

The report says insurgents were responsible for 77 percent of the Afghan civilian deaths. NATO-led and Afghan government forces caused 410 civilian deaths, a decrease of 4 percent from 2010. A further 279 civilian deaths could not be attributed to either the militants or the government forces.

The report said bombs, including roadside mines detonated by people stepping on them or vehicles driving over them, were the "single, largest killer of Afghan children, women and men" in 2011, taking the lives of about one-third of the civilians killed. The death toll from suicide attacks rose dramatically in 2011 to 450, an increase of 80 percent over 2010.

U.N. special representative Jan Kubis said "Afghan children, women and men continue to be killed in this war in ever-increasing numbers."